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1H and 13C NMR spectral data for spiro[2.4]heptadiene-4,6 and spiro[4.4]nonadiene-1,3

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PII: 0022-2364(75)90025-6 JOURNALOFMAGNE'W2RESONANCE 19,31-36(1975) lH and 13C NMR Spectral Data for [email protected]@2,4 96 and Spiro[4.4jnmadiene-I,3 L. J. M. VAN DE VEN AND J. W. DE HAAN Laboratory of Instrumental Analysis, Eindhoven University of Technology, Netherlands Received September 30,1974 ‘H and 13C NMR spectral data have been obtained for spiro[2.4]heptadiene-4,6 and spiro[4.4]nonadiene-1,3, using selective decoupling of proton lines and matching of calculated and experimentally observed spectra. The high-field olefmic proton signals in spiro[4.4Jnonadiene-1,3 are assigned to the “inner” ole&ic protons, The results indicate that comparable ‘H-‘H and 1H-13C coupling constants in the cyclopentadiene parts of both molecules are similar. This indicates similar bond localizations as well. Recently a number of publications appeared concerning the analysis of high- resolution, coupled 13C NMR spectra of 5- and (S-membered he&on&ear aromatic rings (I ). Of the corresponding hydrocarbons only benzene (2) and naphthalene (3) have been analyzed in detail. No complete analyses of cyclopentadiene systems have as yet been published. Here we present ‘H and 13C NMR analyses of spiro[2.4]heptadiene-4,6 (I) and spiro- [4.4Jnonadiene-1,3 (II). Apart from being 5,5-disubstituted cyclopentadiene deriva- tives, these compounds are of special interest because some controversial remarks have 5 4 1 sxl 3 6 7 2 I 2 16 7 Da 5 3 4 9 0 II been made concerning the supposed Spiro-aromaticity of I. In 1970, Clark and Fiato (4) decided that a combination of the cyclopentadienyl anion and the ethenyl cation wifl contribute to the extent of ca 15 %. These arguments have been used in a later stage to dank Press, Inc. 31 iniulyformreserved. 2 32 VAN DE VEN AND DE HAAN explain similar phenomena in related systems (5,6). However, the original conclusions of Clark and Fiato have since then been questioned, based on electron diffraction (7) and MO calcula

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